A suspension arrangement of this type was previously disclosed by the published patent application US 2004/0223062 A1, for example. The application shows a pan-tilt camera system comprising a driving belt sheave and a driven belt sheave, coupled together by a drive belt. According to the embodiment shown in FIG. 5, a further belt sheave is also included for adjusting the tension of the drive belt. However, the suspension arrangement disclosed by the application lacks separate equipment for stabilizing the directional equipment, that is to say in this case the camera, intended to prevent random or periodic movements in the mounting of the suspension arrangement being transmitted to the camera.
Solutions previously known to us for stabilizing directional equipment, but using another drive system, are briefly touched upon below. All of these known solutions used a gyro, which indicates changes of direction.
According to one known solution, the suspension arrangement is driven by electric motors via gearboxes. The servo feedback-coupled to the motors compensates for the change of direction. This solution is not self-compensating since the inherent moment of inertia of the motors in conjunction with the transmission gearing constitutes the dominant load in the compensating movement. This results in a small bandwidth for the stabilization and a high degree of wear.
According to another known solution the suspension arrangement is directly driven by a torque motor. The solution is self-stabilizing and has a wide bandwidth. Disadvantages are that the solution has a low adjusting moment, which results in a susceptibility to bearing friction and also external interference. The torque motor solution is furthermore costly.
Another known suspension arrangement is of a four-axis design or more specifically a biaxial gimbal having a small trimming range enclosed in an outer biaxial gimbal having a large trimming range. The solution is self-stabilizing and robust, and has a large bandwidth. Disadvantages of this solution are that it is bulky and expensive.
A further known solution is to stabilize a mirror in cameras or other optical instruments, for example. The stabilization can be made virtually self-stabilizing by means of a secondary mass. The solution has a large bandwidth. Possible problems may include distortion of the image when panning and the fact that the mirror is itself an environmentally sensitive component.